Field of the Invention:
The invention relates to a slab laser including cooled, mutually parallel electrodes having flat sides or surfaces facing each other and forming a discharge chamber between the sides or surfaces in which a gas to be pumped is located.
Slab or strip conductor lasers are known, for instance, from European Patent Application 0 275 023 A1, corresponding to U.S. Pat. No. 4,719,639 and European Patent Application 0 305 893 A2, corresponding to U.S. Pat. No. 4,939,738. In those lasers, a narrow discharge chamber for a gas, especially CO.sub.2, which is excited by a high-frequency voltage applied to the electrodes, is formed between plate-like electrodes that are parallel to one another. Resonator mirrors are provided opposite end surfaces of the narrow discharge chamber formed by the electrodes to attain a laser effect.
In those known gas lasers, heat that occurs upon pumping and because of the laser action is dissipated by heat conduction through the plate-like electrodes, so that a more-complicated gas circulation system is no longer necessary. That is possible because the electrodes are relatively large in surface area, and their mutual spacing, which is typically a few millimeters, is relatively slight, so that the gas volume enclosed between the electrodes is likewise relatively slight in proportion to the cooling area.
The laser output power obtainable with slab lasers depends on the surface area of the electrodes. Approximately 1.5W to 2.0W of power can be generated per square centimeter of electrode surface area. In order to be able to produce high output power, large-area electrodes are needed, which nevertheless cannot be kept adequately parallel to one another because of their non-uniform heating. Since inner flat surfaces, that is those facing toward the gas or discharge chamber, are heated, while the outer flat surfaces are cooled, a high temperature gradient required for heat dissipation occurs, so that the flat surfaces of an electrode which face each other experience different thermal expansion. That causes bending moments, which in turn cause the electrodes to be spaced farther apart at their ends than in the middle. The resulting distortion of the resonator worsens the laser performance, or in other words its mode stability and mode purity. Since the sagging increases as the electrode length increases, the known lasers cannot attain output power of more than a few hundred watts, because the enlargement of the electrode surfaces is only limitedly possible due to thermal bending.